The exhaust system of an internal combustion engine typically functions to collect the exhaust gases produced by the engine, reduce the noise associated with the exhaust gases to an acceptable level, reduce the levels of certain objectionable pollutants in the exhaust gas and deliver the exhaust gas to an acceptable location for release into the atmosphere. The typical prior art exhaust system for vehicles has comprised a manifold for mounting to the engine and collecting the exhaust gases, a plurality of interconnected pipes, a catalytic converter and at least one muffler. The catalytic converter has comprised a canister having opposed inlet and outlet ends which are connected respectively to pipes of the exhaust system. A catalyst is securely mounted within the canister of the catalytic converter. The catalyst in combination with the heated exhaust gases converts the carbon monoxide, unburned hydrocarbons and nitrous oxides into less objectionable exhaust gases. The catalytic converter becomes operative or "lights-off" after it is heated to a specified temperature by the hot exhaust gases. In view of this lighting-off requirement, the catalytic converter typically is placed as near to the engine as possible to interact with the exhaust gases before any significant cooling takes place. The catalytic converter is known to reach substantially elevated temperatures. As a result, catalytic converters often are provided with heat shields and/or insulation to protect adjacent structures from heat related damage.
The one or more mufflers of the exhaust system function principally to reduce exhaust related noise. The typical prior art exhaust muffler comprises a plurality of tubes which communicate with chambers. In particular, the typical prior art exhaust muffler may comprise at least one tube having perforations, louvers or apertures extending therethrough to permit the exhaust gases to communicate with an expansion chamber. The movement of the exhaust gases through a perforated or louvered tube in communication with an expansion chamber generally attenuates a substantial portion of the exhaust gas noises. In most cases, however, some fairly low frequency noise will remain despite the noise attenuating effects of the perforated or louvered tubes and expansion chamber. These residual low frequency noises often are attenuated by one or more tuning tubes which communicate with the remaining tubes of the muffler and which also communicate with substantially enclosed low frequency resonating chambers. The cross-sectional area and length of the tuning tube and the volume of the associated low frequency resonating chamber are selected in accordance with the specific frequency ranges of the residual low frequency noise to be attenuated.
The typical prior art muffler has comprised a plurality of separate tubular members supported in a parallel array by a plurality of spaced apart transversely disposed baffles. The array of tubes and baffles is mounted within an outer shell of elongated generally tubular configuration having a constant generally circular or elliptical cross section along the length of the outer shell. The dimensions of the various internal components of these prior art mufflers have been largely dictated by the exhaust gas characteristics. These internal dimensional requirements have also partly dictated the external dimensions. However, automotive engineers are also required to fit the muffler in the limited available space on the vehicle. Thus, the overall length and cross-sectional shape of the prior art muffler have been appropriately adjusted within the limits dictated by the internal requirements of the muffler to enable the muffler to fit within the available space on the vehicle. The prior art muffler typically has been merely suspended from the underside of the vehicle at a convenient and acceptable location rearwardly of the engine compartment and spaced from the underside of the vehicle.
The prior art has included attempts to combine some noise attenuating functions into a catalytic converter. For example, U.S. Pat. No. 3,061,416 which issued to Kazokas on Oct. 30, 1962 shows a catalytic muffler with a plurality of different catalysts mounted in generally cylindrical arrays at selected locations throughout the muffler. The acoustical functions of the structure appear to be carried out by arrays of perforations in generally cylindrically mounted tubes. The muffler shown in U.S. Pat. No. 3,061,416 is of generally standard outer shell construction, but with an extremely complex multi-component internal configuration.
Another combined catalytic converter and muffler is shown in U.S. Pat. No. 3,556,735 which issued to Epelman on Jan. 19, 1971. U.S. Pat. No. 3,556,735 includes baffles mounted on rods that extend the entire length of the muffler. Certain of the baffles define chambers within which catalysts are mounted. Another similar structure is shown in U.S. Pat. No. 3,841,841 which issued to Torosian on Oct. 15, 1974.
U.S. Pat. No. 4,626,732 issued to Carboni on Oct. 14, 1986 and shows a combined muffler/catalytic converter having certain stamp formed components. The sound attenuating characteristics of the structure shown in U.S. Pat. No. 4,626,732 are derived from certain stamp formed perforated plates mounted in generally parallel arrays within the structure.
Generally, the above described prior art structures which attempt to combine a catalytic converter with a muffler perform a very limited noise attenuation function by permitting some expansion of exhaust gases through perforated baffles, plates or tubes. The noise attenuation achieved by such structures generally would not be sufficient to meet most new car noise requirements within the United States and many other countries. Thus, if these prior art combined catalytic converters and mufflers could ever be used at all, they would have to be supplemented with a second muffler. Additionally, any attempt to expand the above described and identified prior art catalytic converters/mufflers using the teaching of the prior art would substantially increase the dimensions of those structures. The physical limitations suggested by these prior art structures would make it difficult to physically locate the structure in close proximity to the engine to achieve the desirable quick light-off of the catalyst.
Certain prior art mufflers have been formed partly or entirely from stamp formed components. Until very recently, most prior art stamp formed mufflers have largely performed an exhaust gas expansion function. As a result, these prior art stamp formed mufflers would not adequately attenuate the exhaust gas noises and would often leave residual low frequency noises unattenuated.
Recently, however, substantial improvements to stamp formed exhaust mufflers have been made. In particular, U.S. Pat. No. 4,700,806 and U.S. Pat. No. 4,736,817 issued to Jon Harwood and are assigned to the assignee of the subject application. U.S. Pat. No. 4,700,806 and U.S. Pat. No. 4,736,817 are directed to extremely efficient and effective mufflers that comprise arrays of stamp formed tubes, including tuning tubes, and a plurality of chambers, including expansion chambers and low frequency resonating chambers. Thus, the mufflers shown in U.S. Pat. No. 4,700,806 and in U.S. Pat. No. 4,736,817 perform noise attenuating functions at least as well as, or better than, the typical prior art mufflers, but are formed from many fewer components and can be manufactured and assembled efficiently.
Further improvements in stamp formed mufflers are presented in co-pending applications that are assigned to the assignee of the subject application. In particular, U.S. patent application Ser. No. 061,876, now U.S. Pat. No. 4,760,894 is directed to an "EXHAUST MUFFLER WITH ANGULARLY ALIGNED INLETS AND OUTLETS". U.S. patent application Ser. No. 061,913, now U.S. Pat. No. 4,759,423 is directed to an efficient "TUBE AND CHAMBER CONSTRUCTION FOR AN EXHAUST MUFFLER". U.S. patent application Ser. No. 106,244, now U.S. Pat. No. 4,765,437, is directed to an efficient construction for a "STAMP FORMED MUFFLER WITH MULTIPLE LOW FREQUENCY RESONATING CHAMBERS" which enables plural stamp formed tuning tubes and plural low frequency resonating chambers with a substantially reduced deformation of the stamp formed outer shells. U.S. patent application Ser. No. 146,032, now U.S. Pat. No. 4,821,840, is directed to a "STAMP FORMED MUFFLER WITH CONFORMAL OUTER SHELL" which enables the muffler to efficiently conform to the limited available space on a vehicle rather than constant cross section as in most prior art mufflers. The disclosures of the above identified patents and applications assigned to AP Industries, Inc. are incorporated herein by reference.
Despite the many advantages of the above described stamp formed mufflers and despite the substantial engineering work performed on catalytic converters, there have been no combined mufflers/catalytic converters that have performed both intended functions well and have been widely accepted in the marketplace.
In view of the above, it is an object of the subject invention to provide a combined catalytic converter and muffler.
Another object of the subject invention is to provide an exhaust muffler that securely retains, insulates and protects a catalytic converter.
A further object of the subject invention is to provide a combined catalytic converter and exhaust muffler assembly that adequately tunes and attenuates the noise associated with exhaust gases.
Still another object of the subject invention is to provide a combined catalytic converter and exhaust muffler that can be readily fit into the available space on a vehicle.
Yet another object of the subject invention is to provide a combined catalytic converter and exhaust muffler assembly wherein noise attenuating chambers of the assembly contribute to the heat shielding and insulation of the catalytic converter.
Still an additional object of the subject invention is to provide a combined catalytic converter and exhaust muffler formed substantially from a catalyst and stamp formed components and including stamp formed tubes disposed on opposite sides of the catalytic converter to contribute to heat shielding and insulation.
Another object of the subject invention is to provide an exhaust system which removes pollutants and attenuates noise with a substantial weight reduction over prior art systems.